The present invention relates to passive infra-red motion detectors of the type used in residential outdoor lighting fixtures, for example, to illuminate a walkway or driveway when a person or automobile approaches. The invention is more particularly directed to arrangements for making the motion detector an inconspicuous element of the lighting fixture and to a mirror arrangement suitable for use in such motion detectors.
Lighting fixtures that are activated by passive infra-red (PIR) motion detectors have long been available. PIR motion detectors were first used in the lighting field with utilitarian lighting such as flood lights or other area lighting. These early models employed assemblies of germanium lenses or multi-faceted mirrors or combinations of mirrors and lenses to direct infra-red radiation from an object moving in the field of view to a PIR sensor disposed in a housing. The early housings tended to be bulky and quite conspicuous.
With the development of the flexible plastic segmented Fresnel lens, motion detector housings could be made more compact and much less conspicuous. A Fresnel lens of the sort used in connection with motion detectors comprises a thin sheet of flexible plastic material that permits infra-red radiation to pass through it and on which are formed a number of individual Fresnel lens segments or lenslets. See for example U.S. Pat. No. 3,203,306 to Lefferts for an individual Fresnel lens segment formed on such a plastic sheet and U.S. Pat. No. 4,321,594 to Galvin or U.S. Pat. No. 4,703,171 to Kahl et al. for a segmented Fresnel lens having a plurality of lens segments side-by-side on a plastic sheet.
As motion detectors became more compact and less conspicuous, they were applied to decorative lighting fixtures, as well as utilitarian floodlights, since the distraction from the decorative aspects of the fixture could be held to a tolerable level.
In recent years the trend has been to integrate the motion detector into the decorative light fixture itself to make the motion detector less obtrusive either by concealing it altogether or at least by giving it a decorative appearance so that it does not detract appreciably from the ornamental style of the light fixture. Examples of PIR lighting fixtures that endeavor either to conceal the motion-detecting unit or to embellish it so as to enhance its decorative appearance may be seen in U.S. Pat. Nos. 5,282,118 and 5,434,764 to Lee et al.; U.S. Pat. No. 5,575,557 and U.S. Pat. No. Des. 382,082 to Huang et al.; U.S. Pat. No. 5,590,953 to Haslam et al.; and U.S. Pat. No. 5,626,417 to McCavit.
Typically, the flexible plastic lens was formed to be a part of a wall of some portion of the fixture. This construction may impose a limitation on the lens optics. In decorative fixtures the nature of the fixture bodyxe2x80x94its curvature, slope, profile and overall shapexe2x80x94is chosen primarily by aesthetic considerations to give the fixture its decorative appearance and to some extent by manufacturability considerations to maintain a lower cost. The resulting fixture body design, however, may then constrain the optics of the segmented Fresnel lens, which will generally follow the contour of a wall of the fixture body. That is, the Fresnel lens may be disposed in a fixture wall at an angle or as part of a curved surface in such a manner that it may impair the ability of the lens to focus radiation from a desired direction and in a desired intensity on the sensor. Alternatively, the aesthetic design of the light fixture may be compromised so as to provide a more favorable optical environment for the segmented Fresnel lens.
The present invention provides a motion detector based on mirrored optics that is well suited for use in decorative lighting fixtures in a variety of locations while avoiding the disadvantages of Fresnel lenses and at the same time providing coverage for a very wide field of view that may extend to 360 degrees.
Many of today""s decorative lighting fixtures have design styles deriving from early oil-burning coach or carriage lanterns. Such designs typically contain saucer-shaped design elements that originally served as oil reservoirs, cylindrical design elements that originally served as shields, and stylistically decorated generally axially symmetric cylindrical-like elements, commonly referred to as chimneys, having a number of slots formed in them that originally served as vents. The present invention is able to take advantage of such traditional stylistic elements of decorative lanterns to house a motion detector while avoiding the disadvantages of Fresnel lens optics and without compromising the motion detector field of view.
Briefly, this is achieved with a mirror assembly that may be disposed within decorative elements such as saucers and chimneys that are common elements of lighting fixtures. One or more apertures are defined in the decorative element to admit infra-red radiation, which impinges on the mirror assembly. The mirror assembly comprises a plurality of opaque elongate members that are azimuthally spaced about a central longitudinal axis in such a way as to define an alternating sequence of open elongate slots and opaque elongate members. Each elongate member is formed with a mirror face on its inner surface which is generally facing the central longitudinal axis, and the PIR sensor is also disposed substantially at the longitudinal axis. The elongate members and mirror faces define a plurality of detection zones in the motion detector field of view at two different vertical levels of view, each vertical level of view having a characteristic optical path associated with it. In a first optical path for monitoring the field of view at a first vertical level (the far zone), infra-red radiation passes from an associated zone through one of the slots between two elongate members and is reflected from one of the mirror faces and concentrated onto the sensor. In the second characteristic optical path for monitoring the field of view at a second vertical level (the near zone), infra-red radiation passes from an associated zone through one of the slots and on to the sensor without being deflected by any of the mirror faces. These two types of optical paths may be achieved in a full 360 degree zonal pattern for both the far zone and the near zone.
Various other aspects, advantages, and novel features of the invention are described below or will be readily apparent to those skilled in the art from the following specifications and drawings of illustrative embodiments.